*{
    margin: 0;
    padding: 0;
}
.wrap{
    min-width: 600px;
}

#header,#footer{
    height: 50px;
    width: 100%;
    background: grey;
}

#middle,#left,#right{
    float: left;
}
#left,#right{
    height: 200px;
    width: 200px;
    background: pink;
}
#left{
    margin-left: -100%;
    position: relative;
    left: -200px;
}
#right{
    margin-left: -200px;
    position: relative;
    left: 200px;
    /* position: absolute; */
    /* right: -200px; */
}
#middle{
    width: 100%;
}

#content{
    /* 开辟BFC */
    overflow: hidden;

    padding: 0 200px;
}